Low oil pressure control system for compressors

ABSTRACT

A low oil pressure system for an air compressor control wherein a logic configuration is utilized comprised of a first plurality of NOR gates representing a monostable multivibrator circuitry and another plurality of NOR gates in a NAND arrangement representing an input sensing circuitry. The protection system is operative to render and maintain said compressor inoperable when low oil pressure occurs until the cause of said low pressure is corrected, at which time manual means is utilized to render said compressor operable. The included monostable multivibrator circuitry utilizes a resistance-capacitor discharge circuitry means during manual starting of the compressor to override the said protection system while the oil pressure initially builds up during a no fault condition.

United States Patent 151 3,682,574 Sanders [451 Aug. 8, 1972 LOW OIL PRESSURE CONTROL 3,408,940 ll/1968 McGrogan ..417/12 SYSTEM FOR COMPRESSORS Primary Examiner-William L. Freeh [72] Inventor. Walter J. Sanders, Jeannette, Pa. y p w. Mclmire, JR [73] Assignee: Westinghouse Air Brake Company,

Wilmerding, Pa. 57 ABSTRACT Filed: 1970 A low oil pressure system for an air compressor con- [211 App]. 78,521 trol wherein a logic configuration is utilized comprised of a first plurality of NOR gates representing a monostable multivibrator circuitry and another plu- UsSo of gates in a arrangement I [51] Int. Cl ..F04b 49/00 representing an input sensing circuitry. The protection [58] Field of Search ..123/198 D; 184/64; 417/12, system is operative to render and maintain said 417/13 pressor inoperable when low oil pressure occurs until the cause of said low pressure is corrected, at which [56] References cued time manual means is utilized to render said compres- UNITED STATES PATENTS sor operable. The included monostable multivibrator circuitry utilizes a resistance-capacitor discharge cir- 2,46 1 Yerger ..4 l uiu'y means during manual tarting of the compressor 3,105,629 10/1963 Van Vooren ..417/ 13 to override the said protection system while the i 3,199,523 10/1965 McEa-nhnon "123/198 D pressure initially builds up during a no fault condition. 3,385,278 5/1968 Johnson et a1 ..123/198 D 3,478,731 11/1969 Norton et a1. ..417/13 7 Claims, 2 Drawing Figures TO OIL PUMP LOW on. PRESSURE CONTROL SYSTEM FOR cowmssous BACKGROUND OF INVENTION Air compressor controls must include a means for providing a predetermined lubricating oil pressure during running thereof. If the oil pressure system fails, the compressor must be stopped and maintained stopped until the fault is corrected. During starting operation of the compressor, suflicient allowance for time of buildup of oil pressure must be permitted, thereby creating the need for a protection override system to permit operation of the compressor during a predetermined time for build-up of oil pressure and stopping operation of the compressor after said predetermined time if the oil pressure has not built up to said predetermined pressure.

SUMMARY OF INVENTION According to the present invention there is provided an air compressor protection control including a low oil pressure sensing means utilizing logic devices to render the air compressor inoperative when an oil pressure fault occurs, and maintaining said compressor inoperative until manually started after said oil pressure fault has been corrected; said logic devices comprising a monostable multivibrator circuitry in cooperation with an input sensing circuitry to override the protection control and permitting a running condition for a predetermined time interval during initial starting of the compressor when no oil pressure fault exists, thereby permitting initial oil pressure build-up.

In the accompanying drawing there is shown in FIG. 1, the compressor protection logic circuitry including a monostable multivibrator circuit, and a plurality of NOR logic devices arranged in a NAND configuration to represent an input sensing circuitry.

FIG. 2 shows a driver and latching circuit including a thyristor device utilized for controlling the contacts of a compressor governor.

DESCRIPTION The compressor protection system comprises a plurality of NOR logic devices 1 and 2 shown in dotted outline boxes including circuitry described hereinafter to form a monostable multivibrator circuitry. The monostable multivibrator circuit referred to hereinafter as the m-m circuit includes a pair of transistor devices 3 and 4 making up logic device 1 and a single transistor device 5 making up logic device 2, all of which are interconnected in a manner described hereinafter with an R-C timing circuit comprised of resistances 6 and 7 operative cooperatively with a capacitor 8 to provide a timed output signal at terminal 9.

The protection system further comprises another plurality of NOR logic devices 10 and 11 arranged in a NAND logic configuration to form an input sensing circuitry to control an output signal at driver circuit terminal 12 as controlled by the output signal at terminal 9 via diode 13 to NOR logic device 11. It should be noted that if the logic devices 1 and 2 of FIG. 1 where shown in pure logic form as logic devices 10 and 1 l are, the base terminals to the transistors 3, 4, and 5 would correspond to the input terminals of the logic devices 1 and 2 respectively. A compressor operating switch 14 and an oil pressure switch 15 are connected in the circuitry as described hereinafter.

The output signal at terminal 12 is supplied as shown in FIG. 2 via a wire 16 to the gate terminal of a thyristor driver 17 hereinafter referred to as SCR 17 (Silicon Controlled Rectifier) arranged in series with a DC. supply 18, a normally closed manually operated switch 19, and a solenoid 20, to control a plunger 21 or other means to interrupt closing of governor contacts 22 on the compressor governor 23.

OPERATION Under normal operating conditions, with sufiicient oil pressure, and the compressorrunning the switch 14 closes to provide a logic 1 input signal at terminal 10a of logic device 10 to thereby provide a logic 0" input to terminal 11a of logic device 1 1. With sufficient oil pressure present, the pressure switch 15 is closed to provide a logic l input to terminal 11b of logic device 11 such that the logic device 11 is disabled thereby providing a logic 0 output at terminal 12 to maintain the driver circuit to SCR 17 deenergized in a normal condition to permit normal running of the compressor.

If the oil pressure should fail during a running operation, (the logic 0" input to 11a remaining as just described), the pressure switch 15 would open to provide a logic 0 to terminal 11b of the logic device and along with the normal logic 0 signal from terminal 9 via diode 13 (explained hereinafter), and the logic 0 at terminal 1 1a would thereby enable logic device 11 to provide a logic 1 signal at terminal 12 of the driver circuit. With a logic 1 signal at terminal 12 said signal is supplied via wire 16 to the gate 173 of SCR 17 to overcome the normal negative bias thereto (via resistor 23 and a ground terminal to cause the SCR 17 to conduct. With the SCR 17 conducting, the circuit to the solenoid 20 is completed from the source 18, closed switch 19, solenoid 20, conducting SCR 17 and thence to a ground terminal to thereby energize solenoid 20. With the solenoid 20 energized, the solenoidplunger 21 thereof is inserted between the contacts 22 of a compressor governor 23 (shown in outline) in a manner to prevent restarting of the compressor 24 shown in outline, and if so arranged, in a manner to instantly stop the compressor. Once the cause of the faulty oil pressure has been located and corrected, the manual switch 19 must be opened to permit retracting the plunger 21 from between contacts 22 and permit restarting of the compressor. Prior to buildup of oil pressure during this restarting, the low oil pressure would again cause operation of the driver circuitry and SCR 17 to stop the compressor, however, this is momentarily prevented by the m--m circuitry as follows.

When the compressor is not running, the capacitor 8 is charged from a supply at the supply terminal 25, wire 26, resistor 6, wire 27, capacitor 8 and wire 28 to the base terminal 5b of transistor 5, thereby causing transistor 5 to conduct. \Vrth transistor 5 conducting and the emitter terminal 52 connected by wire 29 to ground, the collector tenninal 5e, wire 30, and terminal 9 are maintained at very close to ground potential, relatively low signal level. Upon starting of the compressor motor, the current responsive switch 14 closes to supply a logic l signal to the base terminal 3b of the transistor 3, to cause said transistor 3 to conduct. Initiation of the signal to transistor 3 effects operation of the monostable multivibrator in a usual well known manner by discharge of the included R-C circuitry as explained briefly herein. With transistor 3 conducting and the emitter terminal 3e connected to ground by wire 29, the charged capacitor 8 will immediately begin to discharge via wire 27, conducting transistor 3 and wire 29 to ground. Since the capacitor 8 is unable to instantaneously discharge, the formerly ground potential of said capacitor on the right-hand side connected to wire 28 will now drop to'a negative potential below ground potential in a manner known in the multivibrator art, thereby causing the transistor 5 to become nonconductive. When the transistor 5 stops conducting, the voltage supplied from terminal 25 to the collector terminal 5c, wire 30 and terminal 9 will be permitted to rise to a relatively high level and be maintained at said high level until the capacitor 8 is discharged and again recharged (as described before) to provide a signal to the base terminal 5b which again causes the transistor to conduct and terminates the high level signal at wire 30 and terminal 9. As long as the high level signal at terminal 9 is maintained, a logic 1 signal is applied via diode 13 to terminal 1 lb of the logic device 1 l to disable the logic device 11 and prevent supply of a signal from terminal 12 to the driver circuitry and SCR 1,7 which in turn prevents stopping of the operation of the compressor as previously described. The time interval. during which the high level signal is maintained at terminal 9 is predetermined according to the time required to normally build-up oil pressure at the compressor, said time interval being regulated by the values of resistor 6 and discharge time of capacitor 8. A latching circuitry from terminal 9 via wire 31 to the base terminal 4b of transistor 4 causes the transistor 4 to conduct and maintain a parallel discharge circuitry for capacitor 8 via transistor 4 while the terminal signal 9 is at high level even though the signal at base terminal 3b may be terminated. It can thus be seen that the time interval required to discharge the capacitor 8 is the time interval of the high level signal at terminal 9 which in turn determines the duration of prevention of operation of the protection system during a starting operation while the oil pressure normally builds up. At the duration of this high level signal at terminal 9, if the oil pressure has not built up to the desired pressure, the signal at terminal 9 (after recharge of capacitor 8) again becomes a low level signal near ground potential as previously explained, and the pressure switch 15 is maintained open due to lack of oil pressure, thereby providing a logic signal to terminal 11b of the logic device 1 l to enable said logic device 1 l and provide a logic 1 signal at terminal 12 and SCR 17 to cause cessation of operation of the compressor in a manner previously described to provide the operative protection desired.

Having now described the invention what I claim as new and desire to secure by Letters Patent, is:

l. A compressor control system for regulating operation of a compressor apparatus only when the lubricating oil pressure thereto is at a predetermined pressure or attaining said pressure during initial starting operation, said system comprising:

a. a compressor governor means for controlling running condition of a compressor,

b. a motor switch means operative responsively to a running condition of said compressor to provide a first logic signal and responsive to a non-running condition of said compressor to provide a second logic signal, g

c. a pressure responsive means conditioned responsively to a high predetermined lubricating oil pressure in said compressor apparatus to provide a first logic signal and responsively to a low predetermined lubricating oil pressure therein to provide a second logic signal,

d. driver circuitry means effective when in a certain energized condition to cause said governor to prevent said running condition of said compressor from occurring, and

logic circuitry means operative responsively to said first logic signal from said motor switch means and to said second logic signal from said pressure responsive means to effect saidcertain energized condition of said driver circuitry means and further operative responsively to said first logic signal from said motor switch means to initiate a timing period during which said logic circuitry means is prevented from effecting said certain energized condition of said driver circuitry means.

2. The apparatus as claimed in claim 1 further characterized in that said logic circuitry includes means operatively responsive to said second logic signal of said motor switch means to prevent energization of said driver circuitry means irrespective of said first or said second logic signal of said pressure responsive means.

3. The apparatus as claimed in claim 1 further characterized in that said driver circuitry means includes a solenoid device operable when energized to mechanically prevent operation of said governor means to prevent a running condition of the compressor.

4. The apparatus as claimed in claim 3 further characterized in that said driver circuitry means includes a thyristor device operable responsively to an.

energizing signal supplied to said driver circuitry to effect energization of said solenoid device.

5. The apparatus as claimed in claim 1 further characterized in that said logic circuitry includes a monostable multivibrator circuit and a signal input sensing circuit.

6. The apparatus as claimed in claim 5 further characterized in that said multivibrator circuit comprises: i

i. a resistor-capacitor charging and discharging branch having a predetermined time constant, and ii. a plurality of transistors operative responsively to receipt of said first logic signal from said motor switch to permit a timed discharge of said resistorcapacitor branch to provide a timed delay signal in parallel with said first logic signal from said motor switch means to disable said input sensing circuit for a period corresponding to said predetermined time constant. 7. The apparatus as claimed in claim 5 further characterized in that said input sensing circuit includes: i. a first logic device operative responsively to said first logic signal from said motor switch to provide a first logic signal output, and

ii. a second logic device operative responsively to said first logic signal output and said second logic signal of said pressure responsive means to provide a second logic signal output for energizing said driver circuitry means, and responsively to said timed delay signal for rendering said second logic signal output ineffective. 

1. A compressor control system for regulating operation of a compressor apparatus only when the lubricating oil pressure thereto is at a predetermined pressure or attaining said pressure during initial starting operation, said system comprising: a. a compressor governor means for controlling running condition of a compressor, b. a motor switch means operative responsively to a running condition of said compressor to provide a first logic signal and responsive to a non-running condition of said compressor to provide a second logic signal, c. a pressure responsive means conditioned responsively to a high predetermined lubrIcating oil pressure in said compressor apparatus to provide a first logic signal and responsively to a low predetermined lubricating oil pressure therein to provide a second logic signal, d. driver circuitry means effective when in a certain energized condition to cause said governor to prevent said running condition of said compressor from occurring, and e. logic circuitry means operative responsively to said first logic signal from said motor switch means and to said second logic signal from said pressure responsive means to effect said certain energized condition of said driver circuitry means and further operative responsively to said first logic signal from said motor switch means to initiate a timing period during which said logic circuitry means is prevented from effecting said certain energized condition of said driver circuitry means.
 2. The apparatus as claimed in claim 1 further characterized in that said logic circuitry includes means operatively responsive to said second logic signal of said motor switch means to prevent energization of said driver circuitry means irrespective of said first or said second logic signal of said pressure responsive means.
 3. The apparatus as claimed in claim 1 further characterized in that said driver circuitry means includes a solenoid device operable when energized to mechanically prevent operation of said governor means to prevent a running condition of the compressor.
 4. The apparatus as claimed in claim 3 further characterized in that said driver circuitry means includes a thyristor device operable responsively to an energizing signal supplied to said driver circuitry to effect energization of said solenoid device.
 5. The apparatus as claimed in claim 1 further characterized in that said logic circuitry includes a monostable multivibrator circuit and a signal input sensing circuit.
 6. The apparatus as claimed in claim 5 further characterized in that said multivibrator circuit comprises: i. a resistor-capacitor charging and discharging branch having a predetermined time constant, and ii. a plurality of transistors operative responsively to receipt of said first logic signal from said motor switch to permit a timed discharge of said resistor-capacitor branch to provide a timed delay signal in parallel with said first logic signal from said motor switch means to disable said input sensing circuit for a period corresponding to said predetermined time constant.
 7. The apparatus as claimed in claim 5 further characterized in that said input sensing circuit includes: i. a first logic device operative responsively to said first logic signal from said motor switch to provide a first logic signal output, and ii. a second logic device operative responsively to said first logic signal output and said second logic signal of said pressure responsive means to provide a second logic signal output for energizing said driver circuitry means, and responsively to said timed delay signal for rendering said second logic signal output ineffective. 